分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： Using data collected with the Belle detector at the KEKB asymmetric-energy e+e− collider, we measure the energy dependence of the e+e−→hb(nP)π+π− (n=1,2) cross sections from thresholds up to 11.02GeV. We find clear Υ(10860) and Υ(11020) peaks with little or no continuum contribution. We study the resonant substructure of the Υ(11020)→hb(nP)π+π− transitions and find evidence that they proceed entirely via the intermediate isovector states Zb(10610) and Zb(10650). The relative fraction of these states is loosely constrained by the current data: the hypothesis that only Zb(10610) is produced is excluded at the level of 3.3 standard deviations, while the hypothesis that only Zb(10650) is produced is not excluded at a significant level.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： We present an extraction of azimuthal correlations between two pairs of charged pions detected in opposite jets from electron-positron annihilation. These correlations may arise from the dependence of the di-pion fragmentation on the polarization of the parent quark in the process e+e−→qq¯. Due to the correlation of the quark polarizations, the cross-section of di-pion pair production, in which the pion pairs are detected in opposite jets in a dijet event, exhibits a modulation in the azimuthal angles of the planes containing the hadron pairs with respect to the production plane. The measurement of this modulation allows access to combinations of fragmentation functions that are sensitive to the quark's transverse polarization and helicity. Within our uncertainties we do not observe a significant signal from the previously unmeasured helicity dependent fragmentation function G⊥1. This measurement uses a dataset of 938~fb−1 collected by the Belle experiment at or near s√≈10.58 GeV.
分类： 物理学 >> 核物理学 提交时间： 2016-09-10
摘要： We report a measurement of the time-dependent CP asymmetry of B0->D(*)CP h0 decays, where the light neutral hadron h0 is a pi0, eta or omega meson, and the neutral D meson is reconstructed in the CP eigenstates K+ K-, K0S pi0 or K0S omega. The measurement is performed combining the final data samples collected at the Y(4S) resonance by the BaBar and Belle experiments at the asymmetric-energy B factories PEP-II at SLAC and KEKB at KEK, respectively. The data samples contain ( 471 +/- 3 ) x 10^6 BB pairs recorded by the BaBar detector and ( 772 +/- 11 ) x 10^6, BB pairs recorded by the Belle detector. We measure the CP asymmetry parameters -eta_f S = +0.66 +/- 0.10 (stat.) +/- 0.06 (syst.) and C = -0.02 +/- 0.07 (stat.) +/- 0.03 (syst.). These results correspond to the first observation of CP violation in B0->D(*)CP h0 decays. The hypothesis of no mixing-induced CP violation is excluded in these decays at the level of 5.4 standard deviations.
分类： 物理学 >> 核物理学 提交时间： 2016-09-09
摘要： We report a measurement of the amplitude ratio rS of B0→D0K∗0 and B0→D0¯K∗0 decays with a model-independent Dalitz plot analysis using D→K0Sπ+π− decays. Using the full data sample of 772×106 BB¯ pairs collected at the Υ(4S) resonance with the Belle detector at KEKB accelerator the upper limit is rS<0.87 at the 68 % confidence level. This result is the first measurement of rS with a model-independent Dalitz analysis, and is consistent with results from other analyses. The value of rS indicates the sensitivity of the decay to ϕ3 because the statistical uncertainty is proportional to 1/rS. The rS result is obtained from observables (x±, y±) x−y−x+y+,====+0.4+1.0+0.0−0.6−0.1±0.0−0.6+0.8+0.1−1.0−0.0±0.1+0.1+0.7+0.0−0.4−0.1±0.1+0.3+0.5+0.0−0.8−0.1±0.1 where x±=rScos(δS±ϕ3), y±=rSsin(δS±ϕ3) and ϕ3(δS) are the weak (strong) phase difference between B0→D0K∗0 and B0→D0¯K∗0. The first uncertainty is statistical, the second is the experimental systematic and the third is the systematic due to the uncertainties on ci and si parameters measured by CLEO.
分类： 物理学 >> 核物理学 提交时间： 2016-08-29
摘要： We report a study of radiative decays of \chi_{bJ}(1P)(J=0,1,2) mesons into 74 hadronic final states comprising charged and neutral pions, kaons, protons; out of these, 41 modes are observed with at least 5 standard deviation significance. Our measurements not only improve the previous measurements by the CLEO Collaboration but also lead to first observations in many new modes. The large sample allows us to probe the total decay width of the \chi_{b0}(1P). In the absence of a statistically significant result, a 90% confidence-level upper limit is set on the width at \Gamma_{total}< 2.4 MeV. Our results are based on 24.7 fb^{-1} of e+e- collision data recorded by the Belle detector at the \Upsilon(2S) resonance, corresponding to (157.8\pm3.6)\times10^6 \Upsilon(2S) decays.
分类： 物理学 >> 核物理学 提交时间： 2016-08-24
摘要： We present a measurement of angular observables, P′4, P′5, P′6, P′8, in the decay B0→K∗(892)0ℓ+ℓ−, where ℓ+ℓ− is either e+e− or μ+μ−. The analysis is performed on a data sample corresponding to an integrated luminosity of 711 fb−1 containing 772×106 BB¯ pairs, collected at the Υ(4S) resonance with the Belle detector at the asymmetric-energy e+e− collider KEKB. Four angular observables, P′4,5,6,8 are extracted in five bins of the invariant mass squared of the lepton system, q2. We compare our results for P′4,5,6,8 with Standard Model predictions including the q2 region in which the LHCb collaboration reported the so-called P′5 anomaly.
分类： 物理学 >> 核物理学 提交时间： 2016-08-23
摘要： We report a measurement of ratio R(D∗)=B(B¯0→D∗+τ−ν¯τ)/B(B¯0→D∗+ℓ−ν¯ℓ), where ℓ denotes an electron or a muon. The results are based on a data sample containing 772×106 BB¯ pairs recorded at the Υ(4S) resonance with the Belle detector at the KEKB e+e− collider. We select a sample of B0B¯0 pairs by reconstructing both B mesons in semileptonic decays to D∗∓ℓ±. We measure R(D∗)=0.302±0.030(stat)±0.011(syst), which is within 1.6σ of the Standard Model theoretical expectation, where σ is the standard deviation including systematic uncertainties.
分类： 物理学 >> 核物理学 提交时间： 2016-08-23
摘要： We report a measurement of the branching fractions of the radiative decays D0→Vγ, where V=ϕ, K¯¯¯¯¯∗0 or ρ0. This is the first observation of the decay D0→ρ0γ. We measure preliminary branching fractions B(D0→ϕγ)=(2.76±0.20±0.08)×10−5, B(D0→K¯¯¯¯¯∗0γ)=(4.66±0.21±0.18)×10−4 and B(D0→ρ0γ)=(1.77±0.30±0.08)×10−5, where the first uncertainty is statistical and the second systematic. We also present the first measurement of CP asymmetry in these decays. The preliminary values are ACP(D0→ϕγ)=−(0.094±0.066±0.001), ACP(D0→K¯¯¯¯¯∗0γ)=−(0.003±0.020±0.000) and ACP(D0→ρ0γ)=0.056±0.151±0.006. The analysis was conducted using 943 fb−1 of data collected by the Belle detector at the KEKB e+e− collider.
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